Conventional chilled water air conditioning systems use chilled water as a working medium to cool an air stream through the action of heat transfer as the air stream comes in close contact with the chilled water in a finned tube heat exchanger commonly referred to as a chilled water cooling coil and herein called the primary cooling coil. Cooling is accomplished by a reduction of temperature in the air stream as the air stream comes in close contact with the fins of the primary cooling coil. The chilled water passes through the tubes of the coil and extracts heat from the air stream. This reduction of temperature is commonly called sensible cooling. A corresponding simultaneous reduction in the moisture content of the air steam typically also occurs to some extent and is known as latent cooling or more generally dehumidification or moisture removal. Usually cooling itself is controlled by means of a thermostat or other type apparatus in the occupied space or in the return air stream which corresponds to changes in the dry bulb air temperature. When controlled in this manner, dehumidification of the indoor air occurs only when there is a demand for reduced temperature as dictated by the thermostat.
Existing standard run-around coil systems typically use a specialized fluid pump to exchange energy between the return and supply air flows of a primary chilled water cooling coil. The energy transfer lowers the air temperature entering the primary coil so that the primary coil can provide a greater amount of latent heat extraction from the air stream. While schemes such as these have been found to be somewhat effective, the specialized fluid pump adds costs and complexity to the system. Also, the specialized fluid pump requires maintenance and can be a source of system failure.
A standard two-pipe air conditioning system 100 is shown in FIG. 1. The two-pipe chilled water air conditioning system 100 shown there includes a housing 110 configured to receive a warm return air flow 120 into the housing and to exhaust the warm return air flow from the housing as a cooled supply air flow 130. The cooled supply air flow might be delivered to an occupied space in a house or commercial building, for example. A cooling coil 140 is disposed in the housing and is configured to permit a working fluid 150 to flow therethrough. The working fluid passing through the cooling coil 140 absorbs thermal energy from the warm return air flow 120 passing through fins or other structures of the cooling coil 140 thereby rendering the cooled supply air flow 130 exiting from the housing 110.
The cooling coil 140 is mechanically and thermally coupled with a plurality of cooling fins (not shown), and is in operative fluid communication with a chilled water source conduit 162 and with a chilled water return conduit 166. The cooling coil 140 receives at an input 142 thereof the working fluid 150 from an associated chilled water source 160 via the chilled water source conduit 162. For completing the fluid circuit, the cooling coil 140 expels at an output 144 thereof the working fluid 150 to an associated chilled water return 164 via the chilled water return conduit 166.
Overall then, the standard two-pipe air conditioning system 100 includes a cooling coil 140 where a working fluid 150 flowing through the cooling coil 140 absorbs thermal energy from a return air flow 120 as a cooled supply air flow 130. A chilled water source conduit 162 delivers the working fluid 150 from an associated chilled water source 160 to the cooling coil 140, and a chilled water return conduit 166 returns the working fluid 150 from the cooling coil 140 to an associated chilled water return 164.
A standard four-pipe air conditioning system 200 is shown in FIG. 2. The four-pipe chilled water air conditioning system 200 shown there includes a housing 210 configured to receive a warm return air flow 220 into the housing 210 and to exhaust the warm return air flow 220 from the housing 210 as a cooled supply air flow 230. The cooled supply air flow 230 might be delivered to an occupied space in a house or commercial building, for example. A cooling coil 240 is disposed in the housing 210 and is configured to permit a cold working fluid 250 to flow therethrough. The cold working fluid 250 passing through the cooling coil 240 absorbs thermal energy from the warm return air flow 220 passing through fins or other structures of the cooling coil 240 thereby rendering the cooled supply air flow 230 exiting from the housing 210.
The cooling coil 240 is mechanically and thermally coupled with a plurality of cooling fins (not shown), and is in operative fluid communication with a chilled water source conduit 262 and with a chilled water return conduit 266. The cooling coil 240 receives at an input 242 thereof the cold working fluid 250 from an associated chilled water source 260 via the chilled water source conduit 262. For completing the cooling fluid circuit, the cooling coil 240 expels at an output 244 thereof the cold working fluid 250 to an associated chilled water return 264 via the chilled water return conduit 266.
To accomplish dehumidification when the thermostat does not indicate a need for cooling, a humidistat or humidity sensor in combination with a controller is often added to control the chilled water flow in order to remove moisture from the cooled air stream as a “byproduct” function of the cooling. In this mode of operation, heat must be selectively added to the cooled air stream to prevent the occupied space from over-cooling below the dry bulb set point temperature or the thermostat. The adding of heat to the cooled air stream is commonly referred to as reheat.
Many sources of heat have been used for reheat purposes, such as hydronic hot water with various fuel sources, hydronic heat recovery sources, gas heat, hot refrigerant gas heat, hot liquid refrigerant heat and electric heat. Electric heat is commonly used because it is typically the least expensive to install. However, the use of electric heat typically is the most expensive to operate and in some instances is precluded from use by local law.
The standard four-pipe air conditioning system 200 as shown in FIG. 2 includes reheat coil 270 disposed in the housing 210 for providing heat to accomplish the reheat function when the system is in the dehumidification mode and when the thermostat does not indicate a need for cooling as described above. The reheat coil 270 is configured to permit a warm working fluid 252 to flow therethrough. As illustrated, the supply air flow 230 includes an upstream supply air flow 232 entering into the reheat coil 270, and a downstream supply air flow 234 exiting from the reheat coil 270. The warm working fluid 252 passing through the reheat coil 270 adds thermal energy into the upstream supply air flow 232 entering into the reheat coil 270 and passing through fins or other structures of the reheat coil 270, thereby providing a warmer reheated downstream supply air flow 234 exiting from the reheat coil 270 and delivered into the working space, for example.
The reheat coil 270 is mechanically and thermally coupled with a plurality of cooling fins (not shown), and is in operative fluid communication with a warm water source conduit 282 and with a warm water return conduit 286. The reheat coil 270 receives at an input 272 thereof the warm working fluid 252 from an associated warm water source 280 via the warm water source conduit 282. For completing the reheating fluid circuit, the reheat coil 270 expels at an output 274 thereof the warm working fluid 252 to an associated warm water return 284 via the warm water return conduit 286.
Overall then, the standard four-pipe air conditioning system 200 includes a cooling coil 240 where a cold working fluid 250 flowing through the cooling coil 240 absorbs thermal energy from a return air flow 220 as a cooled supply air flow 230, and a reheat coil 270 where a warm working fluid 252 flowing through the reheat coil 270 adds thermal energy into the cooled supply air flow 230 as a reheated supply air flow 234. A chilled water source conduit 262 delivers the cold working fluid 250 from an associated chilled water source 260 to the cooling coil 240, and a chilled water return conduit 266 returns the cold working fluid 250 from the cooling coil 240 to an associated chilled water return 264. Similarly, a warm water source conduit 282 delivers the warm working fluid 252 from an associated warm water source 280 to the reheat coil 270, and a warm water return conduit 286 returns the warm working fluid 252 from the reheat coil 270 to an associated warm water return 284.
In order to conserve energy, it has been suggested that recovered heat may be used as a source for the reheat. Accordingly, one method to improve the moisture removal capacity of the primary chilled water coil, while simultaneously providing reheat, is to provide two coils, each in one of the air streams entering or leaving the primary chilled water coil, while circulating a working fluid, often water, between the two coils. This arrangement is commonly call a run-around loop.
The success of these run-around systems is undeniable. The run-around system working fluid is cooled in the first coil, called the reheat coil, which is placed in the supply air stream of the primary coil. The cooled working fluid is then in turn caused to circulate through a second coil, called a precooling coil, placed in the return air stream of the primary coil. The circulation of the run-around system working fluid is provided by a fluid pump which is located in the pipeline connecting the two coils. This simple closed loop circuit comprises the typical run-around systems available heretofore.
FIG. 3 is a schematic view of a unique air conditioning system 300 that has been proposed for use with the single chilled water supply 160 and chilled water return 164 of the standard two-pipe air conditioning system 100 of FIG. 1. The air conditioning system 300 includes a cooling coil 340 where a cold working fluid 350 flowing through the cooling coil 340 absorbs thermal energy from a return air flow 320 as a cooled supply air flow 330, and a reheat coil 370 where a portion of the cold working fluid 350 may circulate. The cooling coil 340 is divided into a primary cooling portion 340′ and a precooling portion 340″. The cold working fluid 350 enters into the primary cooling coil 340′ at an input port 342 of the cooling coil 340 and exits the cooling coil 340 at two (2) exit ports including a first exit port 344′ in fluid communication with the primary cooling coil 340′ portion of the cooling coil 340, and a second exit port 344″ in fluid communication with the precooling coil portion 340″ of the cooling coil 340. The portion of the cold working fluid exiting the cooling coil 340 from the first port 344′ is returned to the chilled water return 364 via a chilled water return conduit 366. The portion of the cold working fluid exiting the cooling coil 340 from the second port 344″ is delivered in part to an input 372 of the reheat coil 370 and in part to a control valve system 390. In the air conditioning system 300 illustrated, the control valve system controls the proportion of chilled working fluid exiting the precooling coil portion 340″ of the cooling coil 340 that is delivered to the reheat coil 370 versus the amount that is returned to the chilled water return 364 thereby effecting control over the reheat circuit.
In general in the subject relevant art, the cooling capacity required of the primary coil is equal to the total cooling required to cool and dehumidify the conditioned space less the amount of cooling provided by the precooling coil. Since the precooling is a function of the amount of reheat used, if there is no demand for reheat, as in a peak sensible cooling demand in the space, then there would be no precooling available to offset the primary cooling capacity required. Therefore, the capacity of the primary coil is based on the total peak cooling load. The capacity of the precooling coil is a function of the amount of heat required for the heat required by the reheat coil.
The heat exchange surface of the precooling and primary cooling coils is selected for their respective peak duties which generally is; peak sensible room cooling for the primary coil and, peak dehumidification for the precooling coil. As such, since these two duties are not simultaneous, the total surface area of the two coils is greater than an optimized coil selected for each of the individual duties.
It has, therefore, been deemed desirable to provide a system that would allow the two coils to share the respective precooling and primary cooling needed to satisfy the various operating conditions representing cooling requirements from peak sensible cooling to dehumidification and that said system will be made compact to conserve space and said system will eliminate the pump of the closed loop run-around system.
It has also been deemed desirable to provide systems and methods that improve on efficiencies and capabilities of the prior systems shown in FIGS. 1-3.